Chicago has become the first city in the United States to ban its restaurants from selling foie gras.
Didier Durand warned of the economic effects of the ban
The French delicacy is made from the livers of force-fed ducks and geese.
The measure, promoted by city councillor Joe Moore, is backed by animal rights lobbyists, but chefs say the council has exceeded its authority.
Some city restaurants launched a lawsuit on Tuesday, and said they would meanwhile continue to serve foie gras, without charging customers for it.
Managers at Cyrano's bistro and wine bar in the River North district say foie gras sales have tripled since news of the ban hit the headlines.
Head chef Didier Durand described the ban as "unfair".
"I have been cooking for 30 years and I feel offended that the city council, not the mayor of Chicago, but the city council took the foie gras away from my hands," he said.
Restaurants say that pending their legal challenge they will offer foie gras as part of a garnish, charging customers only for the garnish, in an attempt to work round the law.
The new ordinance bans only the sale of foie gras, not its consumption.
The Illinois Restaurant Association has now filed a lawsuit in an attempt to stop the law, passed by the city council in April this year.
It argued the City Council has exceeded its authority by seeking to legislate against something that does not occur within the city, or even in the state of Illinois.
Foie gras is the product of torture, say protesters
"Whether the treatment of animals in Canada, France or New York leading to the production of foie gras is or is not humane is not a problem suitable for legislation by the City of Chicago, let alone a substantial Chicago problem," the lawsuit says.
But a spokesman for the council's law department pointed out that Chicago regulates many things - such as guns and fireworks - which are not produced in the city.
Colleen McShane, president of the Illinois Restaurant Association, said the ban was taking away freedom of choice.
"We want to send the city council a strong message, saying when they start to come into our kitchens and mess around with our recipes and menus, we're talking about taste and we're talking about rights and we're talking about freedom of choice."
But sponsors of the new ban say the issue is not one of choice but one of values.
Councillor Moore, the man behind the measure, worked closely with animal rights lobbyists.
Restaurants say they want freedom of choice
Their campaign claims the procedure of force feeding the ducks and geese so that their livers become swollen is akin to torture.
"There is no other food product which requires the torturing of a creature for three to four weeks before that creature is slaughtered and brought to the table," said Councillor Moore.
The city council is confident the law will withstand a legal challenge.